Great to hear, thanks for your help debugging!
I am currently trying to solve the exact same problem. This thread seems to be rather old and I thought that it was merged already, was not it?
I have the default tax rate set in the admin interface (exclusive) and I use an option to add tax for each item (because in such case the whole invoice rate counts tax twice).
The problem is that I need to select tax for each item manually and its not automatically preselected.
My default language is not English (Czech).
The problem is present in InvoiceNinja.com demo.